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Nav Source knob

Printed From: Avidyne
Category: Avidyne General
Forum Name: IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM
Forum Description: Topics on Avidyne's IFD 5 Series and IFD 4 Series Touch Screen GPS/NAV/COM
URL: http://forums.avidyne.com/forum_posts.asp?TID=2608
Printed Date: 18 May 2024 at 7:43am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com


Topic: Nav Source knob
Posted By: cavu
Subject: Nav Source knob
Date Posted: 15 Dec 2023 at 8:42pm
If I select a LPV approach that has LNAV/VNAV and LNAV and circling minima, will turning the Nav Source knob scroll through any of these options?  i.e  disable the glide slope for instance or change the missed approach point.

Never tried it and thought someone might be able to shed light on it.



Replies:
Posted By: vas4avidyne
Date Posted: 18 Dec 2023 at 1:17am
My experience is that you pick a particular RNAV approach (e.g. RNAZ Z Rwy 31 KRHV) and the IFD picks the lowest minimums that it can support for that approach. If LPV minimums are available and the IFD is getting the appropriate GPS signal, you will get a glide slope with the ability to fly down to LPV minimums. 

I have had some situations where it started with the LPV minimums but somewhere along the approach, I received a message about the loss of GPS integrity and it "downgraded" to LNAV minimums. In some other cases, it gave me only the LNAV minimums even though there were LPV minimums published for the approach. In my specific case, it seemed to be related to my antenna - once I cleaned it, those issues seem to have gone away.

I guess the other way of looking at it is that you can decide what minimum you want to use for the approach (LPV or LNAV or circling). If LPV minimums are available, you will get a glide slope but you can choose to terminate your approach at the MDA dictated by the LNAV or circling minimum. As far as I know, the missed approach procedure on an RNAV approach with different published minimums is the same regardless of whether you did the approach to LPV, LNAV or circling minimums.

Vas




Posted By: cavu
Date Posted: 20 Dec 2023 at 3:50pm
Thanks, that's a very good rely.

I did not get a message on the IFD that the GPS integrity was lost while on the LPV (and the GS dropped out).  I did get the message when I selected the LPV into another airport.  It only showed the L/VNAV selection.

I did a little more investigation and there was a solar flare episode shortly before I began the LPV approach. 

The antennas look clean.  How dirty was yours (or how dirty is dirty)  to cause this?

Thanks again.


Posted By: vas4avidyne
Date Posted: 20 Dec 2023 at 5:08pm
You're very welcome! There was nothing obvious on the antenna connections when I opened it up. I just used an electronics cleaning agent and cleaned all the surfaces before putting it back. As best as I can tell, things have improved since then. 

There was one approach (RNAV 32 at KSTS) that initially had this problem (in low IMC for good measure) and the LNAV minimum was higher than the reported ceiling so I landed up doing a missed approach and coming back to do the ILS. I haven't had a chance to try it again there.

I've heard that local conditions could also cause the "downgrade" from LPV to LNAV minimums (like your solar flare example).

Vas



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